One use for a progressing cavity pump is as a well pump. A progressing cavity pump has a stator with an elastomeric liner in its interior. The liner has a passage through it that has a helical contour. A helical rotor, typically of metal, locates within the stator and is rotatable relative to it. Rotating the rotor causes the well fluid to pump through the stator.
In one type of installation, the stator is secured to the lower end of a string of tubing that is suspended in the well. The rotor is secured to a string of drive rods and lowered through the tubing into the stator. After reaching the lowermost point, the operator lifts the rods and rotor a short distance to properly align the rotor with the stator. The drive rods are driven by a drive source at the surface, typically a bearing box and electrical motor. As the well fluid fills the tubing, the rods will stretch to some extent due to the weight of the well fluid. The rotor will thus move downward a short distance relative to the stator.
Some wells produce a combination of liquid and gas. The gas entrained within the liquid is detrimental to the efficiency of the progressing pump. Gas separators have been utilized with electrical submersible well pumps for many years. One type of gas separator has a rotating member, typically a set of vanes that spins with the pump to impart centrifugal force to the well fluid. The centrifugal force results in the heavier components flowing to the outer portion and the lighter components are gas remaining in the center. A crossover member at the top diverts the gas out into the casing and directs the liquid component up into the pump.
The centrifugal pump is made up of a large number of stages of impellers and diffusers. A centrifugal pump is not driven by rods and does not experience any downward movement of the drive shaft as a result of the weight of liquid in the tubing.
Progressing cavity pumps with gas separators are known, both for rod-driven types as well as the type that utilizes a downhole submersible electrical motor to drive the rotor. However, provisions to accommodate the rod stretch for the rod-driven type are not known in the prior art.